Can arrhythmias cause major sleep disturbances nightly? (i have already been tested for apnea and night seizures and have differing results...).

Not directly: Arrhythmias will not cause major sleep disturbances directly unless you are having significant pauses in rate or decreased cardiac output. Medications for heart disease (or other diseases) can cause sleep disorders. If your cardiologist clears you of these concerns, get a sleep study (polysomnogram) and have it interpreted by a specialist in sleep medicine.

Yes: Especially benign paroxysmal tachycardia (pat) which can cause awakenings, can be caused by sleep apnea, and is worse when sleeping on the left side. Perhaps some of my other colleagues can also shed some light on this issue.